Pilot for gas burner

ABSTRACT

A pilot for a large capacity gas burner which uses a fixed metering orifice instead of an adjustable needle valve to produce a constant and reliable flame for igniting a relatively large capacity gas burner.

United States Patent Alms et al. 1 Feb. 29, B972 [54] [56] Reign-cr mesCifled [72] Inventors: Erhard E. Alms, Harrington; James E. NITED STATESPATENTS Mmhell Cary bah 3,055,145 9/1962 Lindsay ..263/1 9 A [73]Assignee: AFE Industries, 1lnc., Lake Zurich, Ill. by 3,109,431 11/1963hn "263/19 A said Mitchell 3,273,621 9/1966 Childl'ee ..263/l9 A3,376,862 4 1968 hl 122 Filed: Mar. 18, 1970 Rm 126/2 X [21 AppL 20,543Primary ExaminerEdward G. Favors Attorney-Charles F. Voytech [52]U.S.Cl. ..263/19 A, 431/283,431/285 [57] ABSTRACT [Sl] Int. Cl ..F23l9/04 53 Field of Search ..263/l9 A; 431/283, 285, 158, A W10t a largePally gas whl'ch uses fixed 431/353 tering orifice instead of anadjustable needle valve to produce a constant and reliable flame forigniting a relatively large capacity gas burner.

2 Claims, 4 Drawing Figures 1 T Um f Cu, 2 a

fi A

3 m mmmf P l w m/ 9 Patented Feb. 29, 11k:

PILOT FOR GAS BURNER This invention relates to pilots for large heatcapacity gas burners.

The automatic and continuous processing of agricultural and industrialproducts at times requires a large supply of air heated to ,apredetermined temperature. The source of the heated air may be a gasburner the temperature of the flame of which is considerably higher thanthe temperature desired in the heated air, and hence the products ofcombustion of the bumer are mixed with a stream of air suppiied by a fanor blower. The capacity of the burner is selected to handle peak loadsand hence, for average loads, an on-off operation of the burner andblower is effected. This requires that the burner be periodically litand extinguished throughout the processing operation, and this, in turn,requires the use of a reliable pilot to ignite the burner unfailinglyevery time heat is called for. In prior pilot designs, the gas for thepilot was supplied from a tube or pipe through an adjustable needlevalve. It was felt that each installation of the pilot required adifferent quantity of gas to insure continuous operation of the pilot,and hence the needle valve was provided to permit regulating thequantity of gas supplied to the pilot flame. However, the operation ofthe pilot was found to be erratic and no adjustment of the valve wouldcure this defect.

An object of this invention is to provide a pilot for a gas burnerwherein the pilot will function uniformly under variable conditions ofoperation of the gas burner and of the air supplied thereto.

As a more specific object this invention has within its purview'theprovision of a pilot for a gas burner which is simpler to construct andmaintain and hence less expensive than pilots heretofore designed.

It is also an object of this invention to provide a pilot for a gasburner wherein the pilot requires no adjustment as to the quantity ofgas burned by said pilot, the quantity being determined by a fixedmetering orifice through which the said gas is fed to the pilot.

These and other objects of the invention will become apparent from thefollowing detailed description of a preferred embodiment thereof whentaken together with the accompanying drawings in which:

FIG. 1 is a fragmentary section through the prior art pilot valve withan adjustable needle valve;

FIG. 2 is a section through a pilot burner and associated ig niter andother components of this invention, the section being taken along line22 of FIG. 3;

FIG. 3 is an end elevation of the pilot burner of FIG. 2; and

FIG. 4 is a schematic diagram of a typical installation of a pilot ofthis invention.

For purposes of illustration, this invention will be described withreference to a pilot burner used with automated grain dryers which usepropane gas as a fuel and a powerful fan for (l) supplying air to theburning gas, (2) mixing the hot products of combustion with air toreduce to a safe level the temperature of the heated air contacting thegrain, and (3) creating a pressure differential across the grain columnin the dryer to promote passage of the hot air through the grain. Thepilot burner is ignited once for each continuous run of the dryer, butduring such run, the fan and main burner may be periodically turned onand off as dictated by an appropriate control in the dryer to preventoverheating of the grain. After the grain has been heated and dried, itmust be cooled, while in the dryer by using only the fan, the burnerbeing shut off during this cooling cycle. The pilot burner musttherefore remain lit under both full fan and still fan conditions, andunder full fan with and without burner operation.

The pilot burner is located in a housing in which are also located athermocouple which senses whether the pilot has been ignited, and anelectric igniter for igniting the pilot. Also enclosed in the samehousing is a gas jet which is turned on with the main burner and assistsin igniting the latter.

The environment in which the pilot valve of this invention is designedto operate is shown in FIG. 4. The dryer 47 may be of the type disclosedin U.S. Pat. No. 3,056,214, granted to A.

Andersen, Jr. on Oct. 2, I962. Said dryer has a cylindrical burnersection 48 in which is located a. high-capacity gas burner 49 and a fan50 driven by a motor 51. Fan St supplies outside to the dryer aftermixing with the hot products of combustion of burner 49. The pilotassembly 52 is disposed adjacent burner 49 with its axis crosswise tothe airstream from fan 50.

Referring now to the drawings for a detailed description of the pilotvalve, there will be described first the prior art needle valve shown inFIG. 1, In that Figure, the pilot valve as adapted for use with graindryers is shown at 10 and is comprised of a T"-shaped fitting 11 havingan internal thread 112 at one end and an internal thread 13 at its otherend. Said other end is closed by a plug M which is threaded to cooperatewith internal threads 13, said plug having a flange 15 by which it islocated against the end of fitting lll.

Piug 14 has a central axial orifice Id at the end of a conical seat 17which cooperates with the conical point I3 of a needle valve 19. Saidvalve 119 has an enlarged threaded end 20 which cooperates with internalthreads 12 for adjusting the position of conical end 18 relative to seat17 whereby to adjust the flow of gas to the orifice 16. The inlet to thefitting 111 is at 21 and said inlet is connected to a suitable supply ofpropane gas (not shown).

Air for combustion is supplied to the gas issuing from orifice 16 in amixing chamber 22 formed by a tube 45 threaded over exterior threads 23on fitting I0, said chamber 22 having air inlet openings 24 adjacentplug 14, and outlet openings in the closed end 46 consisting of acentral large opening 25 and a series of smaller angularly disposedopenings 26 surrounding the central opening 25, the burning gas and airmixture being disposed outside of tube 45.

When installed in a grain dryer, for example, the pilot assembly of FIG.l is disposed with the axis of the pilot transverse to the generaldirection of movement of air from the fan 50 through the burner $9, Thefan, and the burner ignited by the pilot assembly of FIG. l, areintermittently operated so that the pilot is exposed to full fanconditions at one time and at another, to still fan conditions.Furthermore, during the cooling cycle of the grain dryer, the fan andthe pilot may be on, but the burner will be off, so that the pilot mustoperate under three extreme conditions.

It has been found that the operation of the pilot of FIG. 1 is erraticin that it will go out at unexpected times, and when the pilot ceases tofunction, the main burner cannot be relit. The sensing of a lack offlame in the pilot by a thermocouple, to be described hereinafter inconnection with FIG. 3, causes a shutdown of the burner as a safetymeasure, and this, in turn, causes a shutdown of the entire dryingmechanism. Diligent investigation of the pilot of FIG. ll failed todisclose any reason for the erratic behavior of the pilot.

I have found that the erratic behavior of the pilot can be corrected byeliminating pilot valve 19. A pilot assembly so made is disclosed inFIGS. 2 and 3. In these Figures, the inlet for the gas for the pilot iscomprised of a straight tube 27 which is externally threaded at bothends to receive at one end a fitting 28 by which the tube is connectedto an appropriate pipe or tube leading to the source of propane gas, andto receive at its other end the mixing chamber 22. A plug 29 is threadedinto the end of tube 27, said plug having an orifice 30 centrallylocated therein, the length of the orifice being determined by acounterbore 3i adjacent orifice 30. Although counterbore 31 is taperedat its end adjacent orifice 30, the taper is not used as a seat for avalve as in the FIG. 1 design.

Tube 27 is secured to a casting 32 through which it extends, saidcasting supporting a tubular housing 33, the righbhand end of which isof reduced conical form 3%, leaving a relatively large opening 35 forthe pilot flame.

The pilot tube 27 is located excentrically of the housing 33, thecentral position within the housing being occupied by a second gas inlettube 36 which is connected to the main gas burner (not shown) so thatwhenever the main gas burner is turned on, tube 36 will be filled withgas, Said tube 36 is closed at its right-hand end by a cap 37 threadedthereon and in which is formed a relatively large orifice 38 throughwhich gas from the interior of tube 36 flows into the opening 35 inhousing 33. it is contemplated that gas issuing from orifice 38 will beignited by the flame fromthe openings 25 and 26 of the pilot mixingchamber 22 and will assist in igniting the main burner.

The pilot is ignited by a pair of electrodes 39, 40 which are of knownconstruction and are retained in appropriate fittings 41 threadedlyreceived in casting 32. A thermocouple 42 extends inwardly adjacent theopenings 25 and 26 in a known manner to sense whether the pilot is lit.Said thermocouple is connected to the controls of the dryer (not shown)to shut the dryer down in the event the pilot is not lit. Air for thecombustion of the pilot gas is supplied through openings 43 in housing33 adjacent openings 24 in mixing chamber 22, said openings 43 inhousing 33 being shielded by one or more scoops 44 which promote theentry of air from the fan of the dryer into the openings 43.

The fixed orifice design of pilot shown in FIGS. 2 and 3 has been foundto provide a steady pilot flame under all operating conditions of thedryer including full fan, still fan, and full fan with and without fullburner. Although it is not known why the absence of the needle valveshould cure the erratic behavior of the prior art pilot, it is surmisedthat the needle valve in some way changed its position relative toorifice l6 and at times obstructed the flow of gas through the orifice,so that by eliminating the needle valve, the obstruction was alsoeliminated. It is understood, of course, that the size of the orifice 30in FIG. 2 is calculated to provide the proper flow of gas into mixingchamber 22.

We claim:

1. A pilot for a gas burner comprising a tube having an inlet openingfor combustible gas, an outlet opening for the tube comprising a fixedorifice in direct constant communication with the interior of the tube,and an air-and-gas mixing chamber adjacent the orifice, a housing forthe pilot having an opening for the flame produced by the pilot, anintermittently operable gas burner in the housing adapted to be ignitedby the pilot, and a gas burner of greater capacity than the first saidgas burner and disposed to emit gas at right angles to the direction ofthe first said gas burner, said gas burner of greater capacity beingsubstantially ignited by the flame from the first said gas burner.

2. A pilot as described in claim 1, said housing being substantiallycylindrical around said pilot and frustoconical around the flameproduced by said pilot, and means creating a variable stream of airmoving across said housing transversely of the axis of said pilot.

lOlOZS 027i

1. A pilot for a gas burner comprising a tube having an inlet openingfor combustible gas, an outlet opening for the tube comprising a fixedorifice in direct constant communication with the interior of the tube,and an air-and-gas mixing chamber adjacent the orifice, a housing forthe pilot having an opening for the flame produced by the pilot, anintermittently operable gas burner in the housing adapted to be ignitedby the pilot, and a gas burner of greater capacity than the first saidgas burner and disposed to emit gas at right angles to the direction ofthe first said gas burner, said gas burner of greater capacity beingsubstantially ignited by the flame from the first said gas burner.
 2. Apilot as described in claim 1, said housing being substantiallycylindrical around said pilot and frustoconical around the flameproduced by said pilot, and means creating a vaRiable stream of airmoving across said housing transversely of the axis of said pilot.